Positive type resist composition and resist pattern formation method using same

ABSTRACT

There is provided a positive type resin composition comprising (A) a resin component comprising within the principal chain a structural unit derived from a (meth)acrylate ester and incorporating an acid dissociable, dissolution inhibiting group containing a polycyclic group on an ester side chain section, for which the solubility in alkali increases under the action of acid, (B) an acid generator component which generates acid on exposure, and (C) an organic solvent, wherein the component (A) comprises both a structural unit derived from a methacrylate ester and a structural unit derived from an acrylate ester. According to such a resist composition, a resist pattern can be formed which displays little surface roughness and line edge roughness on etching, and also offers excellent resolution and a wide depth of focus range.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/004,798, filed on Dec. 7, 2004, entitled “POSITIVE TYPE RESISTCOMPOSITION AND RESIST PATTERN FORMATION METHOD USING SAME,” which is acontinuation of U.S. patent application Ser. No. 10/467,130, filed onAug. 1, 2003, entitled “POSITIVE TYPE RESIST COMPOSITION AND RESISTPATTERN FORMATION METHOD USING SAME.”

TECHNICAL FIELD

The present invention relates to a positive type resist composition, andmore specifically relates to a chemically amplified positive type resistcomposition for use with a wavelength of no more than 200 nm, andparticularly an ArF excimer laser.

BACKGROUND ART

Until recently, polyhydroxystyrenes or derivatives thereof in which thehydroxyl groups are protected with an acid dissociable, dissolutioninhibiting group, which display high transparency relative to a KrFexcimer laser (248 nm), have been used as the base resin component ofchemically amplified resists.

However, these days, the miniaturization of semiconductor elements hasprogressed even further, and the development of processes using ArFexcimer lasers (193 nm) is being vigorously pursued.

For processes using an ArF excimer laser as the light source, resinscomprising a benzene ring such as the polyhydroxystyrenes describedabove have insufficient transparency relative to the ArF excimer laser(193 nm).

Consequently, resins capable of resolving this problem, containing nobenzene rings, and comprising a structural unit derived from a(meth)acrylate ester incorporating a polycyclic hydrocarbon ring such asan adamantane ring within the principal chain are attractingconsiderable interest, and many materials have already been proposed(Japanese Patent (Granted) Publication No. 2881969, Japanese UnexaminedPatent Application, First Publication No. Hei 5-346668, JapaneseUnexamined Patent Application, First Publication No. Hei 7-234511,Japanese Unexamined Patent Application, First Publication No. Hei9-73173, Japanese Unexamined Patent Application, First Publication No.Hei 9-90637, Japanese Unexamined Patent Application, First PublicationNo. Hei 10-161313, Japanese Unexamined Patent Application, FirstPublication No. Hei 10-319595 and Japanese Unexamined PatentApplication, First Publication No. Hei 11-12326).

However, with the development of different etching films in recentyears, a variety of etching gases can now be used, and as a result, anew problem has arisen in that surface roughness appears on the resistfilm following etching.

This surface roughness is different from one which conventional dryetching resistance meet, and in a film etched using a resist pattern asa mask, appears as distortions around the hole patterns in a contacthole pattern, or as line edge roughness in a line and space pattern.Line edge roughness refers to non-uniform irregularities in the lineside walls.

Furthermore, in addition to the surface roughness described above, lineedge roughness also occurs in the resist pattern following developing.

This line edge roughness also appears as distortions around the holepatterns in a contact hole pattern or as non-uniform irregularities inthe line side walls in a line and space pattern.

In addition, the design rules required in modern semiconductor elementproduction continue to become more stringent, and a resolution of nomore than 150 nm, and in the vicinity of 100 nm is now required. As aresult, further improvements in resolution are needed.

Furthermore, in addition to this improvement in resolution, widening ofthe depth of focus range characteristics is also desirable.

However, with conventional resist compositions, resolving the aboveproblems has been unsatisfactory, and further improvements have beenkeenly sought.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a chemically amplifiedpositive type resist composition which displays little surface roughnesson etching and little line edge roughness of the resist patternfollowing developing, and also offers excellent resolution and a widedepth of focus range, as well as a resist pattern formation method whichuses such a composition.

Taking the above circumstances into consideration and as a result ofintensive investigations, the inventors of the present inventiondiscovered that by using a resin comprising both a structural unitderived from a methacrylate ester and a structural unit derived from anacrylate ester as a base resin component, the above problems could beresolved, and were hence able to complete the present invention.

In other words, a positive type resist composition of the presentinvention is a positive type resist composition comprising (A) a resincomponent comprising within the principal chain a structural unitderived from a (meth)acrylate ester and incorporating an aciddissociable, dissolution inhibiting group containing a polycyclic groupon an ester side chain section, for which the solubility in alkaliincreases under the action of acid, (B) an acid generator componentwhich generates acid on exposure, and (C) an organic solvent (C),

wherein the component (A) comprises both a structural unit derived froma methacrylate ester (hereafter this unit may be abbreviated as a“methacrylate ester structural unit”) and a structural unit derived froman acrylate ester (hereafter this unit may be abbreviated as an“acrylate ester structural unit”).

The term “(meth)acrylate” refers to either one, or both of acrylates andmethacrylates. Furthermore, the term “structural unit” refers to amonomer unit which contributes to the formation of a polymer.

A method of forming a resist pattern according to the present inventioncomprises the steps of applying a positive type resist composition ofthe present invention to a substrate, conducting a prebake, performingselective exposure, then conducting PEB (post exposure baking), andperforming alkali developing to form a resist pattern.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a more detailed description of the present invention.

In the component (A), the action of the acid generated from thecomponent (B) on exposure causes the aforementioned highly etchingresistant, acid dissociable, dissolution inhibiting group containing apolycyclic group to dissociate, and the entire component (A) changesfrom an alkali insoluble state to an alkali soluble state.

Consequently, when exposure is conducted through a mask pattern duringthe formation of a resist pattern, the exposed sections of thecomposition display a significant increase in solubility relative toalkali, enabling alkali developing to be used.

In the component (A), the term “comprising both a methacrylate esterstructural unit and an acrylate ester structural unit” means that thereare no particular restrictions on the form of the component, providedthe component (A) incorporates both a methacrylate ester structural unitand an acrylate ester structural unit. For example, the component (A)may be a material comprising a copolymer (A1): a copolymer comprising amethacrylate ester structural unit and an acrylate ester structuralunit, or may be a material comprising a mixed resin (A2): a mixed resinof a polymer comprising at least a methacrylate ester structural unitand a polymer comprising at least an acrylate ester structural unit.Either one, or both of the polymers which constitute this mixed resin(A2) may be a copolymer which corresponds with the copolymer (A1).

Furthermore, other resin components may also be added to the component(A) provided such addition does not impair the effects of the presentinvention, although in the present invention, a component (A) formedfrom either one, or both of the aforementioned copolymer (A1) and theaforementioned mixed resin (A2) is preferred.

In addition, for both the copolymer (A1) and the mixed resin (A2), acombination of two or more different materials can also be used.

The relative quantities of the methacrylate ester structural unit andthe acrylate ester structural unit within the component (A) are suchthat relative to the combined number of mols of the methacrylate esterstructural unit and the acrylate ester structural unit, the methacrylateester structural unit account for 10 to 85 mol %, and preferably from 20to 80 mol %, and the acrylate ester structural unit account for 15 to 90mol % and preferably from 20 to 80 mol %.

If the quantity of the methacrylate ester structural unit is overlylarge then the effect in improving the surface roughness is reduced,whereas if the quantity of the acrylate ester structural unit is overlylarge, there is a danger of a reduction in resolution.

In addition, the component (A) may also be formed from a combination ofa plurality of monomer units with different functions, provided theaforementioned methacrylate ester structural unit and the acrylate esterstructural unit are incorporated within one of the monomer units.

For example, the component (A) can be ideally formed from:

(i) a structural unit derived from a (meth)acrylate ester, andcomprising an acid dissociable, dissolution inhibiting group containinga polycyclic group (hereafter, also referred to as a first structuralunit),

(ii) a structural unit derived from a (meth)acrylate ester, andcomprising a lactone containing monocyclic group or polycyclic group(wherein the term “cyclic group” within the expression “monocyclic groupor polycyclic group” includes a lactone group) (hereafter, also referredto as a second structural unit), and

(iii) a structural unit derived from a (meth)acrylate ester, andcomprising a hydroxyl group containing polycyclic group (hereafter, alsoreferred to as a third structural unit).

In this description and the accompanying claims, the term “lactonecontaining monocyclic group or polycyclic group” refers to a monocyclicgroup formed from a lactone ring or a polycyclic group containing alactone ring. Here, a lactone ring refers to a single ring comprising a—CO—O— structure, and this is counted as the first ring. Accordingly, inthe case of a group with only a lactone ring, the name “lactonecontaining monocyclic group” is used, whereas in the case of a groupwhich also contains other ring structures, the name “lactone containingpolycyclic group” is used regardless of the structure of the otherrings.

In such a case, the first structural unit is essential, and althoughcombinations of the first structural unit with either the secondstructural unit or the third structural unit are acceptable, componentscomprising all three of the first through third structural units arepreferred in terms of etching resistance, resolution, and adhesionbetween the resist film and the substrate. A resin which consists of thefirst through third structural units is more preferable.

In addition, for a component (A) which also comprises a structural unitdescribed below (hereafter also referred to as a fourth structural unit,or as a structural unit (a4)):

(iv) a structural unit derived from a (meth)acrylate ester, andcomprising a polycyclic group which is different from the aciddissociable, dissolution inhibiting group containing a polycyclic groupof the first structural unit, the lactone containing monocyclic group orpolycyclic group of the second structural unit, or the hydroxyl groupcontaining polycyclic group of the third structural unit,

the resolution for isolated patterns through to semi dense patterns(line and space patterns in which for a line width of 1, the space widthis within a range from 1.2 to 2) is excellent, and is preferred.

Accordingly, the actual combination of the first structural unit throughto the fourth structural unit can be adjusted appropriately inaccordance with the desired characteristics and the like.

The component (A) preferably comprises either one, or both of:

a structural unit (a1) derived from an acrylate ester, and comprising anacid dissociable, dissolution inhibiting group containing a polycyclicgroup, and

a structural unit (a1′) derived from a methacrylate ester, andcomprising an acid dissociable, dissolution inhibiting group containinga polycyclic group.

If the structural unit derived from a (meth)acrylate ester, andcomprising an acid dissociable, dissolution inhibiting group containinga polycyclic group incorporates both the aforementioned structural unit(a1) and the aforementioned structural unit (a1′), then the resolutionimproves, which is preferred.

In those cases in which both structural units are present, the molarratio of structural unit (a1): structural unit (a1′) is typically withina range from 0.4 to 2.5, and preferably from 0.6 to 1.5 in order toensure superior co-solubility of the polymer with the structural unit(a1) and the polymer with the structural unit (a1′).

Furthermore, the component (A) also preferably comprises either one, orboth of:

a structural unit (a2) derived from an acrylate ester, and comprising alactone containing monocyclic group or polycyclic group, and

a structural unit (a2′) derived from a methacrylate ester, andcomprising a lactone containing monocyclic group or polycyclic group.

The case in which the structural unit derived from a (meth)acrylateester, and comprising a lactone containing monocyclic group orpolycyclic group incorporates both the aforementioned structural unit(a2) and the aforementioned structural unit (a2′) is preferred.

In those cases in which both of the above structural units are present,the molar ratio of structural unit (a2): structural unit (a2′) istypically within a range from 0.2 to 5.0, and preferably from 0.6 to 1.5in order to ensure superior co-solubility of the polymer with thestructural unit (a2) and the polymer with the structural unit (a2′).

In addition, the component (A) also preferably comprises either one, orboth of:

a structural unit (a3) derived from an acrylate ester, and comprising ahydroxyl group containing polycyclic group, and

a structural unit (a3′) derived from a methacrylate ester, andcomprising a hydroxyl group containing polycyclic group.

The case in which the structural unit derived from a (meth)acrylateester, and comprising a hydroxyl group containing polycyclic groupincorporates both the aforementioned structural unit (a3) and theaforementioned structural unit (a3′) is preferred.

In those cases in which both of the above structural units are present,the molar ratio of structural unit (a3): structural unit (a3′) istypically within a range from 0.2 to 5.0, and preferably from 0.6 to 1.5in order to ensure superior co-solubility of the polymer with thestructural unit (a3) and the polymer with the structural unit (a3′).

Furthermore of the three pairs of combinations, namely, the pair of thestructural units (a1) and (a1′), the pair of the structural units (a2)and (a2′) and the pair of the structural units (a3) and (a3′),components comprising at least 2 pairs are preferred, and componentscomprising all 3 pairs are even more desirable.

In the structural units (a1) and (a1′), examples of the polycyclic groupinclude groups in which one hydrogen atom is removed from abicycloalkane, a tricycloalkane or a tetracycloalkane.

Specific examples include groups in which one hydrogen atom is removedfrom a polycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane.

These types of polycyclic groups can be selected appropriately from themultitude of these types of groups that have been proposed for use withArF resists.

Of these groups, adamantyl groups, norbornyl groups andtetracyclododecanyl groups are preferred from an industrial viewpoint.

Furthermore, there are no particular restrictions on the aforementionedacid dissociable, dissolution inhibiting group, provided that prior toexposure it produces an alkali dissolution inhibiting effect which makesthe entire component (A) insoluble in alkali, and following exposure itdissociates through the action of the acid generated from the component(B), converting the entire component (A) to an alkali soluble state.

Typical examples include cyclic or chain type tertiary alkyl estersformed with the carboxyl group of (meth)acrylic acid.

Provided the structural units (a1), (a1′) have the functions describedabove then there are no particular restrictions on the structural units,although cases in which the acid dissociable, dissolution inhibitinggroup containing a polycyclic group within either one or both (andpreferably both) of the structural units (a1) and (a1′) is selected fromthe general formulas (I), (II) and (III) shown below are preferred, assuch units display excellent resolution and dry etching resistance.

(wherein, R¹ represents a lower alkyl group)

(wherein, R² and R³ each represent, independently, a lower alkyl group)

(wherein, R⁴ represents a tertiary alkyl group)

Specifically, either one or both (and preferably both) of the structuralunits (a1) and (a1′) are preferably at least one type of structural unitselected from the general formulas (I′), (II′) and (III′) shown below.

(wherein, R represents a hydrogen atom or a methyl group, and R¹represents a lower alkyl group, so that the group represents thestructural unit (a1) when R is a hydrogen atom, and the structural unit(a1′) when R is a methyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R² and R³each represent, independently, a lower alkyl group, so that the grouprepresents the structural unit (a1) when R is a hydrogen atom, and thestructural unit (a1′) when R is a methyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R⁴represents a tertiary alkyl group, so that the group represents thestructural unit (a1) when R is a hydrogen atom, and the structural unit(a1′) when R is a methyl group).

The structural unit represented by the general formula (I′) aboverepresents the case in which the carbon atom adjacent to the oxygen atom(—O—) of a (meth)acrylic acid ester section is a tertiary alkyl group ona cyclic skeleton such as an adamantyl group.

Furthermore, in the general formulas (I) and (I′), R is either ahydrogen atom or a methyl group.

In addition, the group R¹ is preferably a lower straight chain orbranched alkyl group of 1 to 5 carbon atoms, and suitable examplesinclude methyl groups, ethyl groups, propyl groups, isopropyl groups,n-butyl groups, isobutyl groups, tert-butyl groups, pentyl groups,isopentyl groups and neopentyl groups. Of these, alkyl groups of atleast 2 carbon atoms, and preferably of 2 to 5 carbon atoms arepreferred, and in such cases, the acid dissociability tends to increasecompared with the case in which R¹ is a methyl group. However incontrast, from an industrial viewpoint, methyl groups are the mostdesirable.

The structural unit represented by the general formula (II′) representsthe case in which the carbon atom adjacent to the oxygen atom (—O—) of a(meth)acrylic acid ester section is a tertiary alkyl group, and a cyclicskeleton such as an adamantyl group exists within this tertiary alkylgroup.

In the general formulas (II) and (II′), R represents the same meaning asin the general formulas (I) and (I′).

Furthermore, R² and R³ each preferably represent, independently, a loweralkyl group of 1 to 5 carbon atoms. These types of groups tend todisplay a higher acid dissociability than a 2-methyl-2-adamantyl group.

Specifically, the groups R² and R³ represent, independently, the sametypes of straight chain or branched alkyl groups described above for R¹.Of these groups, the case in which R² and R³ are both methyl groups ispreferred industrially.

The structural unit represented by the general formula (III′) representsthe case in which the carbon atom adjacent to the oxygen atom (—O—) of aseparate ester section from the (meth)acrylate ester section is atertiary alkyl group, and the separate ester section and the(meth)acrylate ester section are linked with a cyclic skeleton such as atetracyclododecanyl group.

In the general formulas (III) and (III′), R represents the same meaningas in the general formulas (I) and (I′).

Furthermore, R⁴ is a tertiary alkyl group such as a tert-butyl group ora tert-amyl group, although structural units in which R⁴ is a tert-butylgroup are preferred industrially.

In particular, the use of either one or both (and preferably both) ofthe structural units represented by the general formulas (I) and (I)′ ispreferred, and the case in which R¹ is a methyl group, and R² and R³ areboth methyl groups offers particularly good resolution, and isconsequently preferred.

In the structural units (a2) and (a2′), the lactone functional groupsare effective in increasing the adhesion between the resist film and asubstrate, and in improving the affinity with the developing liquid.

There are no particular restrictions on the structural units (a2) and(a2′), provided this type of lactone group containing monocyclic groupor polycyclic group is present.

A specific example of a lactone containing monocyclic group is a groupin which one hydrogen atom is removed from □-butyrolactone.

Furthermore, specific examples of lactone containing polycyclic groupsinclude groups in which one hydrogen atom is removed from a lactonecontaining bicycloalkane of one of the structural formulas shown below.

In addition, in either one or both (and preferably both) of thestructural unit (a2) and the structural unit (a2′), the lactonecontaining monocyclic group or polycyclic group is preferably at leastone structure selected from the general formulas (IV) or (V) shownbelow.

Specific examples of the structural units (a2) and (a2′) includestructural units derived from a (meth)acrylate ester comprising either alactone group or a lactone containing bicycloalkyl group, as shown bythe structural formulas below.

(wherein R is as described above)

(wherein R is as described above)

(wherein R is as described above)

Of these, □-butyrolactone esters or norbornane lactone esters of(meth)acrylic acid with an ester linkage at the □ carbon atom areparticularly preferred in terms of industrial availability.

Because the hydroxyl group within the structural units (a3) and (a3′) isa polar group, by using these structural units, the overall affinity ofthe resin component (A) with the developing liquid improves, and thealkali solubility within the exposed sections improves. Accordingly, thestructural units (a3) and (a3′) contribute to improved resolution.

In the structural units (a3) and (a3′), the polycyclic group can beselected appropriately from the same plurality of polycyclic groupsdescribed in relation to the aforementioned structural units (a1) and(a1′).

There are no particular restrictions on these structural units (a3) and(a3′) provided they are hydroxyl group containing polycyclic groups, andspecific examples of preferred structures include hydroxyl groupcontaining adamantyl groups.

In addition, if this hydroxyl group containing adamantyl group is of astructure represented by a general formula (VI) shown below, then thedry etching resistance can be improved, and the verticalness of thepattern cross-section can be improved, both of which are desirable.

Specifically, cases in which either one or both (and preferably both) ofthe structural units (a3) and (a3′) are structural units represented bythe general formula (VI′) shown below are preferred.

(wherein, R is as described above)

Components (A) in which, relative to the combined total of all thestructural units which make up the component (A), the combined total ofthe structural unit (a1) and the structural unit (a1′) accounts for 30to 60 mol %, and preferably from 30 to 50 mol %, offer superiorresolution, and are consequently preferred.

Furthermore, components (A) in which, relative to the combined total ofall the structural units which make up the component (A), the combinedtotal of the structural unit (a2) and the structural unit (a2′) accountsfor 20 to 60 mol %, and preferably from 20 to 50 mol %, offer superiorresolution, and are consequently preferred.

Furthermore, components (A) in which, relative to the combined total ofall the structural units which make up the component (A), the combinedtotal of the structural unit (a3) and the structural unit (a3′) accountsfor 1 to 50 mol %, and preferably from 20 to 40 mol %, offer superiorresist pattern formation, and are consequently preferred.

In addition, for the aforementioned copolymer (A1), a copolymer (a)described below offers excellent resolution, and is preferred.

Copolymer (a): a copolymer formed from the aforementioned structuralunit (a1′), the aforementioned structural unit (a2′) and theaforementioned structural unit (a3).

In this copolymer (a), from the viewpoints of resolution and resistpattern formation, copolymers in which the structural unit (a1′)accounts for 30 to 60 mol %, and preferably from 30 to 50 mol %, thestructural unit (a2′) accounts for 20 to 60 mol %, and preferably from20 to 50 mol %, and the structural unit (a3) accounts for 1 to 50 mol %,and preferably from 20 to 40 mol %, relative to the combined total ofthe structural units (a1′), (a2′), and (a3), are preferred.

Furthermore, for the aforementioned mixed resin (A2), a mixed resin of acopolymer (b) described below and a copolymer (c) described belowenables a good balance between improved etching resistance (surfaceroughness) and resolution, and is preferred.

Copolymer (b): a copolymer formed from 30 to 60 mol % of theaforementioned structural unit (a1), 20 to 60 mol % of theaforementioned structural unit (a2), and 1 to 50 mol %, and preferablyfrom 5 to 40 mol % of the structural unit (a3).

Copolymer (c): a copolymer formed from 30 to 60 mol % of the structuralunit (a1′), 20 to 60 mol % of the structural unit (a2′), and 1 to 50mol, and preferably from 5 to 40 mol % of the aforementioned structuralunit (a3′).

Furthermore in this mixed resin, the mass ratio between the copolymer(b) and the copolymer (c) is preferably within a range from 80:20 to20:80.

In the copolymers (b) and (c), the incorporation of the structural unit(a3) and the structural unit (a3′) respectively may also be optional.

However, by including either one or both (and preferably both) of thestructural unit (a3) and the structural unit (a3′), because the hydroxylgroup is a polar group, as described above, the overall affinity of theresin component (A) with the developing liquid improves, the alkalisolubility within the exposed sections improves, and the structuralunits also contribute to improved resolution, all of which aredesirable.

Furthermore, for the mixed resin (A2), a mixed resin of the copolymer(a) described above and the copolymer (b) described above also enables agood balance between improved etching resistance (surface roughness) andresolution, and is consequently preferred.

In this mixed resin, the mass ratio between the copolymer (a) and thecopolymer (b) is preferably within a range from 80:20 to 20:80.

In the copolymer (b), the incorporation of the structural unit (a3) mayalso be optional, although including the structural unit (a3)contributes to improved resolution, and is consequently preferred.

Furthermore, for the aforementioned copolymer (A1), a copolymer (d)described below also offers superior resolution, and little surfaceroughness during etching, and is consequently preferred.

Copolymer (d): a copolymer formed from 30 to 60 mol %, and preferablyfrom 30 to 50 mol % of the structural unit (a1′), 20 to 60 mol %, andpreferably from 20 to 50 mol % of the aforementioned structural unit(a2), and 1 to 50 mol %, and preferably from 20 to 40 mol % of thestructural unit (a3).

Furthermore as described above, the component (A) also preferablycomprises, as a fourth structural unit, a structural unit [a structuralunit (a4)] derived from a (meth)acrylate ester, and comprising apolycyclic group “which is different from the aforementioned aciddissociable, dissolution inhibiting group containing a polycyclic group,the aforementioned lactone containing monocyclic group or polycyclicgroup, or the aforementioned hydroxyl group containing polycyclicgroup”.

The expression “which is different from the aforementioned aciddissociable, dissolution inhibiting group containing a polycyclic group,the aforementioned lactone containing monocyclic group or polycyclicgroup, or the aforementioned hydroxyl group containing polycyclic group”means that the polycyclic group of the structural unit (a4) does notduplicate any of the acid dissociable, dissolution inhibiting groupcontaining a polycyclic group of the first structural unit, the lactonecontaining monocyclic group or polycyclic group of the second structuralunit, nor the hydroxyl group containing polycyclic group of the thirdstructural unit. In other words, the structural unit (a4) does notretain any acid dissociable, dissolution inhibiting groups containing apolycyclic group of the first structural unit, any lactone containingmonocyclic groups or polycyclic groups of the second structural unit,nor any hydroxyl group containing polycyclic groups of the thirdstructural unit.

There are no particular restrictions on this type of polycyclic group,provided that the polycyclic group is selected so that within a singlecomponent (A), no duplication occurs of the first through thirdstructural units. For example, the polycyclic group can utilize the samepolycyclic groups described above in relation to the structural units(a1) and (a1′), and any of the multitude of materials conventionallyused as ArF positive resist materials can be used.

In particular, at least one polycyclic group selected from amongtricyclodecanyl groups, adamantyl groups and tetracyclododecanyl groupsis preferred because of the commmercial availability of such groups.

For the structural unit (a4), a single component (A) may also compriseeither one, or both of, a unit derived from an acrylate ester, and aunit derived from a methacrylate ester.

Specifically, the structural unit (a4) may be one of the structuralunits used of the copolymer (A1) as described above, or at least one ofthe structural units of the 1 or more resins which make up the mixedresin (A2), although from the viewpoint of the effects gained, thestructural unit (a4) is preferably incorporated as a unit within acopolymer, together with the first though third structural units.

Specific examples of the structural unit (a4) are shown below.

(wherein, R is a hydrogen atom or a methyl group)

(wherein, R is a hydrogen atom or a methyl group)

(wherein, R is a hydrogen atom or a methyl group)

If the proportion of the structural unit (a4) relative to the combinedtotal of all the structural units of the component (A) is within a rangefrom 1 to 25 mol %, and preferably from 10 to 20 mol %, then theresolution for isolated patterns through to semi dense patterns isexcellent, which is preferred.

Furthermore, in those cases in which the structural unit (a4) isincluded, if the copolymer (A1) is a copolymer (e) described below, thenin addition to the effects of the unit (a4) described above, the surfaceroughness and line edge roughness during etching also improves, which isdesirable.

Copolymer (e): a copolymer formed from the structural unit (a1′), thestructural unit (a2), the structural unit (a3), and the structural unit(a4).

In this copolymer (e), from the viewpoints of resolution and resistpattern formation, copolymers in which the structural unit (a1′)accounts for 30 to 60 mol %, and preferably from 30 to 50 mol %, thestructural unit (a2) accounts for 20 to 60 mol %, and preferably from 20to 50 mol %, the structural unit (a3) accounts for 1 to 30 mol %, andpreferably from 10 to 20 mol %, and the structural unit (a4) accountsfor 1 to 25 mol %, and preferably from 10 to 20 mol %, relative to thecombined total of the structural units (a1′), (a2), (a3) and (a4), arepreferred.

In addition, if the mixed resin (A2) is a mixed resin of theaforementioned copolymer (d) and the copolymer (e), then the resolutionof an isolated space pattern (trench) can be preferred, which isdesirable.

Furthermore in this mixed resin, the mass ratio between the copolymer(d) and the copolymer (e) is preferably within a range from 80:20 to20:80.

In the copolymers (d) and (e), the incorporation of the structural unit(a3) and the structural unit (a3′) may also be optional.

However, by including either one or both (and preferably both) of thestructural unit (a3) and the structural unit (a3′), because the hydroxylgroup is a polar group, as described above, the overall affinity of theresin component (A) with the developing liquid improves, the alkalisolubility within the exposed sections improves, and the structuralunits also contribute to improved resolution, all of which aredesirable.

In addition, in the component (A) there are no particular restrictionson the mass average molecular weight of either the copolymer (A1), orthe polymers which make up the resin mixture (A2), although values aretypically within a range from 5000 to 30,000, and preferably from 8000to 20,000. If the mass average molecular weight is larger than thisrange then solubility within the resist solvent deteriorates, whereas ifthe molecular weight is too small, there is a danger of a deteriorationin the cross-sectional shape of the resist pattern.

The copolymer (A1) or the polymers of the mixed resin (A2) can beproduced easily by a known radical polymerization or the like of thecorresponding (meth)acrylate ester monomer using a radicalpolymerization initiator such as azobisisobutyronitrile (AIBN).

The acid generator component (B) can be appropriately selected fromknown materials used as acid generators in conventional chemicallyamplified resists.

Examples of the acid generator include onium salts such asdiphenyliodonium trifluoromethanesulfonate,(4-methoxyphenyl)phenyliodonium trifluoromethanesulfonate,bis(p-tert-butylphenyl)iodonium trifluoromethanesulfonate,triphenylsulfonium trifluoromethanesulfonate,(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,(4-methylphenyl)diphenylsulfonium nonafluorobutanesulfonate,(p-tert-butylphenyl)diphenylsulfonium trifluoromethanesulfonate,diphenyliodonium nonafluorobutanesulfonate,bis(p-tert-butylphenyl)iodonium nonafluorobutanesulfonate andtriphenylsulfonium nonafluorobutanesulfonate. Of these, onium salts witha fluorinated alkylsulfonate ion as the anion are preferred.

This component (B) may utilize a single compound, or a combination oftwo or more compounds.

The quantity of the component (B) is preferably selected within a rangefrom 0.5 to 30 parts by mass, and even more preferably from 1 to 10parts by mass per 100 parts by mass of the resin component (A). If thequantity is less than 0.5 parts by mass then there is a danger of thepattern formation not proceeding satisfactorily, whereas if the quantityexceeds 30 parts by mass, then achieving a uniform solution becomesdifficult, and there is a danger of a deterioration in storagestability.

In addition, a positive type resist composition of the present inventionis produced by dissolving the component (A), the component (B) and anoptional component (D), which is described below, preferably in anorganic solvent (C).

The organic solvent (C) can be any solvent capable of dissolving thecomponent (A) and the component (B) to generate a uniform solution, andthe solvent used can be one, or two or more solvents selected fromamongst known solvents used for conventional chemically amplifiedresists.

Examples of the solvent include ketones such as acetone, methyl ethylketone, cyclohexanone, methyl isoamyl ketone and 2-heptanone; polyhydricalcohols and derivatives thereof such as ethylene glycol, ethyleneglycol monoacetate, diethylene glycol, diethylene glycol monoacetate,propylene glycol, propylene glycol monoacetate, dipropylene glycol, orthe monomethyl ether, monoethyl ether, monopropyl ether, monobutyl etheror monophenyl ether of dipropylene glycol monoacetate; cyclic etherssuch as dioxane; and esters such as methyl lactate, ethyl lactate,methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethylpyruvate, methyl methoxypropionate, and ethyl ethoxypropionate. Theseorganic solvents can be used singularly, or as a mixed solvent of two ormore solvents.

In particular, mixed solvents of propylene glycol monomethyl etheracetate (PGMEA) and a polar solvent containing a hydroxyl group orlactone such as propylene glycol monomethyl ether (PGME), ethyl lactate(EL) or □-butyrolactone offer good improvement in the storage stabilityof the positive type resin composition, and are consequently preferred.

In those cases in which EL is used, the mass ratio of PGMEA:EL ispreferably within a range from 6:4 to 4:6.

In those cases in which PGME is used, the mass ratio of PGMEA:PGME istypically within a range from 8:2 to 2:8, and preferably from 8:2 to5:5.

Mixed solvents of PGMEA and PGME improve the storage stability in thosecases in which a component (A) which comprises all of the first throughfourth structural units is used, and are consequently preferred.

Mixed solvents containing at least one of PGMEA and ethyl lactate,together with □-butyrolactone are also preferred as the organic solvent(C). In such cases, the mass ratio of the former and latter componentsin the mixed solvent is preferably within a range from 70:30 to 95:5.

Furthermore, in a positive type resist composition of the presentinvention, in order to improve the resist pattern shape and the postexposure stability of the latent image formed by the pattem-wiseexposure of the resist layer, a secondary lower aliphatic amine or atertiary lower aliphatic amine (D) can also be added as an optionalcomponent (D).

Here, a lower aliphatic amine refers to an alkyl amine or an alkylalcohol amine of no more than 5 carbon atoms, and examples of thesesecondary and tertiary amines include trimethylamine, diethylamine,triethylamine, di-n-propylamine, tri-n-propylamine, tripentylamine,diethanolamine and triethanolamine, and alkanolamines such astriethanolamine are preferred.

These may be used singularly, or in combinations of two or morecompounds.

These types of amines are typically added in quantities within a rangefrom 0.01 to 0.2 mass % relative to the quantity of the component (A).

Miscible additives can also be added to a positive type resistcomposition of the present invention according to need, includingadditive resins for improving the properties of the resist film,surfactants for improving the ease of application, dissolutioninhibitors, plasticizers, stabilizers, colorants and halation preventionagents.

A pattern formation method of the present invention can be conducted,for example, in the manner described below.

Namely, a positive type resist composition of the present invention isfirst applied to the surface of a substrate such as a silicon waferusing a spinner or the like, a prebake is conducted under temperatureconditions of 80 to 150□ C for 40 to 120 seconds, and preferably for 60to 90 seconds, and then following selective exposure of an ArF excimerlaser through a desired mask pattern using, for example, an ArF exposureapparatus, PEB (post exposure baking) is conducted under temperatureconditions of 80 to 150□ C for 40 to 120 seconds, and preferably for 60to 90 seconds. Subsequently, developing is conducted using an alkalideveloping liquid such as a 0.1 to 10 mass % aqueous solution oftetramethylammonium hydroxide. In this manner, a resist pattern which isfaithful to the mask pattern can be obtained.

An organic or inorganic anti-reflective film may also be providedbetween the substrate and the applied layer of the resist composition.

Furthermore, although a composition of the present invention isparticularly applicable to ArF excimer lasers, it is also effective forother types of radiation of shorter wavelength such as F₂ lasers, EUV(extreme ultraviolet radiation), VUV (vacuum ultraviolet radiation),electron beams, X-rays and soft X-rays.

In the present invention, by using this type of configuration, achemically amplified positive type resist composition which displayslittle surface roughness or line edge roughness on etching, and alsooffers excellent resolution and a wide depth of focus range can beobtained.

The reasons for these effects are not entirely clear, but are believedto be as follows.

Namely, it is thought that structural units derived from methacrylateesters display excellent lithography characteristics such as resolutionand depth of focus, but tend to display increased surface roughness.

In contrast, it is thought that structural units derived from acrylateesters display a large surface roughness improvement effect but theirlithography characteristics such as the resolution tend to beunsatisfactory.

The fact that structural units derived from acrylate esters probablycontribute towards improvements in the surface roughness was firstdiscovered by the inventors of the present invention, and had previouslybeen unknown.

Accordingly, by using a base resin (the component (A)) comprising acombination of a structural unit derived from a methacrylate ester and astructural unit derived from an acrylate ester, it is surmised that theshortcomings of both can be offset, and a resin displaying the benefitsof both can be produced.

Furthermore, in a positive type resist composition of the presentinvention, in addition to the effects which might be expected based onthe characteristics of these two types of structural unit, an additionalreduction in defects is also achieved. Here, the term “defect” refers toscum and general resist pattern abnormalities detected by inspection ofa resist pattern following developing, from directly above the resistpattern, using a surface defect inspection device (brand name: KLA) fromKLA Tencor Corporation.

EXAMPLES

As follows is a more detailed description of the present invention usinga series of examples.

Example 1

A positive type resist composition was produced by dissolving acomponent (A), a component (B) and a component (D) uniformly in acomponent (C), all of which are described below.

-   Component (A): A mixed resin comprising 50 parts by mass of an    acrylate ester based copolymer (mass average molecular weight:    14,000) formed from structural units x, y and z shown below (x=40    mol %, y=30 mol %, z=30 mol %),    and 50 parts by mass of a methacrylate ester based copolymer (mass    average molecular weight: 10,000) formed from structural units p, q    and l shown below (p=40 mol %, q=40 mol %, l=20 mol %).-   Component (B): 3 parts by mass of triphenylsulfonium    nonafluorobutanesulfonate-   Component (C): A mixed solvent of 450 parts by mass of propylene    glycol monomethyl ether acetate and 300 parts by mass of ethyl    lactate.-   Component (D): 0.2 parts by mass of triethanolamine.

Subsequently, this positive type resist composition was applied to thesurface of a silicon wafer using a spinner, prebaked for 90 seconds at120□ C on a hotplate, and then dried to form a resist layer with a filmthickness of 400 nm.

This film was then selectively irradiated with an ArF excimer laser (193nm) through a mask pattern, using an ArF exposure apparatus (Micro Step,manufactured by ISI Corporation, NA (numerical aperture) =0.60, □=0.75).

The film was then subjected to PEB treatment at 110□ C for 90 seconds,subsequently subjected to puddle development for 60 seconds at 23□ C ina 2.38 mass % aqueous solution of tetramethylammonium hydroxide, and wasthen washed for 20 seconds with water, and dried.

As a result, a 130 nm resist line pattern (1:1) was formed with goodshape, and the depth of focus range was 700 nm.

Furthermore, when the 3□ value, which is a measure of the line edgeroughness of the line and space pattern, was determined, the result was6.3 nm.

The 3□ value is determined by measuring the resist pattern width of thesample at 32 positions using a measuring SEM (S-9220, a brand name,manufactured by Hitachi, Ltd.), and calculating the value of 3 times thestandard deviation (3□) from these measurement results. The smaller this3□ value is, the lower the level of roughness, indicating a resistpattern with a uniform width.

With regard to defects, a resist hole pattern with a hole diameter of250 nm was inspected using a surface defect inspection device KLA2132from KLA Tencor Corporation, and revealed 0 defects.

In addition, in order to evaluate the surface roughness followingetching, an unpatterned resist film was prepared (by applying a positivetype resist composition to a substrate and conducting exposure withoutusing a mask pattern), and subsequently etched under the followingconditions.

-   Etching Conditions

Gas: A mixed gas comprising tetrafluoromethane: 30 sccm,trifluoromethane: 30 sccm, and helium: 100 sccm.

Pressure: 0.3 Torr

RF (Radio frequency): Frequency: 400 kHz, output: 600 W

Temperature: 20□ C, time: 2 minutes

Etching apparatus: TCE-7612X (a brand name, manufactured by Tokyo OhkaKogyo Co., Ltd.)

The reason for performing the evaluation using an unpatterned resistfilm is that this enables surface roughness to be measured more easily.

The surface following this etching was numericalized with an AFM (AtomicForce Microscope), and when the Rms value (root mean square surfaceroughness), which is a value representing the surface roughness, wasthen determined, the result was 2.5 nm.

Example 2

With the exception of altering the component (A) in the manner describedbelow, a positive type resist composition was prepared, and patternformation was conducted, in the same manner as Example 1.

-   Component (A): A mixed resin comprising a polymer (mass average    molecular weight: 15,000) in which the structural units y and z    within the acrylate ester based copolymer used in Example 1 were    altered to 50 mol % and 20 mol % respectively, and the structural    unit x was replaced with 30 mol % of a structural unit m shown    below, and

a polymer (mass average molecular weight: 10,000) in which thestructural unit q within the methacrylate ester based copolymer used inExample 1 was replaced with a structural unit n shown below. Theproportions of the structural units p, n and l were the same as theproportions of the structural units p, q and l respectively used inExample 1.

As a result, a 130 nm line and space pattern (1:1) was formed with goodshape, and the depth of focus range was 700 nm. Furthermore,determination of the 3□ value revealed a result of 5.8 nm.

Inspection for defects was also conducted in the same manner as Example1, and revealed 0 defects.

Furthermore, evaluation of the surface roughness in the same manner asExample 1 revealed an Rms value of 2.2 nm.

Example 3

With the exception of altering the component (A) in the manner describedbelow, a positive type resist composition was prepared, and patternformation was conducted, in the same manner as Example 1.

-   Component (A): A mixed resin comprising 50 parts by mass of the    acrylate ester based copolymer used in Example 1 (mass average    molecular weight: 14,000), and

50 parts by mass of an acrylate ester/methacrylate ester copolymer(wherein the structural unit 1 in the methacrylate ester based copolymerof Example 1 was replaced with the same mol % of the correspondingacrylate ester derivative) (mass average molecular weight: 10,000).

As a result, a 130 nm line and space pattern (1:1) was formed with goodshape, and the depth of focus range was 600 nm. Furthermore,determination of the 3□ value revealed a result of 5.9 nm.

Inspection for defects was also conducted in the same manner as Example1, and revealed 0 defects.

Furthermore, evaluation of the surface roughness in the same manner asExample 1 revealed an Rms value of 2.0 nm.

Example 4

With the exception of altering the component (A) in the manner describedbelow, a positive type resist composition was prepared, and patternformation was conducted, in the same manner as Example 1.

-   Component (A): 100 parts by mass of an acrylate ester/methacrylate    ester copolymer (wherein the acrylate ester copolymer from Example 1    was not used, and the structural unit 1 in the methacrylate ester    based copolymer of Example 1 was replaced with the same mol % of the    corresponding acrylate ester) (mass average molecular weight:    10,000).

As a result, a 130 nm line and space pattern (1:1) was formed with goodshape, and the depth of focus range was 800 nm. Furthermore,determination of the 3□ value revealed a result of 6.8 nm.

Inspection for defects was also conducted in the same manner as Example1, and revealed 0 defects.

Furthermore, evaluation of the surface roughness in the same manner asExample 1 revealed an Rms value of 2.5 nm.

Comparative Example 1

With the exception of altering the component (A) in the manner describedbelow, a positive type resist composition was prepared, and patternformation was conducted, in the same manner as Example 1.

-   Component (A): 100 parts by mass of only the methacrylate ester    copolymer used in Example 1.

As a result, a 130 nm line and space pattern (1:1) was formed with goodshape, although the depth of focus range was 500 nm. Furthermore,determination of the 3□ value revealed a result of 14.0 nm.

Inspection for defects was also conducted in the same manner as Example1, and revealed 0 defects.

Furthermore, evaluation of the surface roughness in the same manner asExample 1 revealed an Rms value of 12.8 nm.

Comparative Example 2

With the exception of altering the component (A) in the manner describedbelow, a positive type resist composition was prepared, and patternformation was conducted, in the same manner as Example 1.

-   Component (A): 100 parts by mass of only the acrylate ester    copolymer used in Example 1.

As a result, a 130 nm line and space pattern (1:1) was formed with goodshape, although the depth of focus range was 200 nm. Furthermore,determination of the 3□ value revealed a result of 3.7 nm.

Inspection for defects was also conducted in the same manner as Example1, and revealed 500 defects.

Furthermore, evaluation of the surface roughness in the same manner asExample 1 revealed an Rms value of 1.1 nm.

From the above results it is evident that in each of the examplesaccording to the present invention, the shape of the line and spacepattern was good, the depth of focus range was large, line edgeroughness was minimal, and absolutely no defects were observed.

In contrast, in Comparative Example 1 which used a base resin formedfrom only methacrylate ester structural units, line edge roughness andsurface roughness were large, whereas in Comparative Example 2 whichused a base resin formed from only acrylate ester structural units, thedepth of focus range was small and a multitude of defects were observed.

Example 5

A positive type resist composition was produced by dissolving acomponent (A), a component (B), a component (D) and an additiveuniformly in a component (C), all of which are described below.

-   Component (A): 100 parts by mass of an acrylate ester/methacrylate    ester copolymer (mass average molecular weight: 10,000,    polydispersity: 1.80) formed from structural units x, y, z and p    shown below (x=35 mol %, y=40 mol %, z=15 mol %, p=10 mol %).-   Component (B): 3.5 parts by mass of triphenylsulfonium    nonafluorobutanesulfonate-   Component (D): 0.3 parts by mass of triethanolamine.-   Additive: 0.1 parts by mass of a fluorine/silicon based surfactant    R08 (manufactured by Dainippon Ink and Chemicals, Inc.).-   Component (C): A mixed solvent of 450 parts by mass of PGMEA, 300    parts by mass of PGME, and 25 parts by mass of □-butyrolactone.

An organic anti-reflective film AR-19 (manufactured by Shipley Co.,Ltd.) (film thickness: 82 nm) was provided on top of a silicon wafer,and the positive type resist composition described above was then coatedonto this anti-reflective film on the silicon wafer using a spinner.

Subsequently, the positive type resist composition was dried for 90seconds at 95□ C on a hotplate (pre bake) to form a resist layer with afilm thickness of 330 nm.

This film was then selectively irradiated with an ArF excimer laser (193nm) through a mask, using an ArF exposure apparatus S302 (manufacturedby Nikon Corporation, NA=0.60), subjected to PEB treatment at 95□ C for90 seconds, subsequently subjected to puddle development for 30 secondsat 23□ C in a 2.38 mass % aqueous solution of tetramethylammoniumhydroxide, and was then washed for 20 seconds with water, and dried.

The 100 nm isolated line pattern formed by the above operation wasformed with good shape, the sensitivity was 23 mJ/cm², and the depth offocus range was 450 nm. Furthermore, the limiting resolution of theisolated line pattern was 60 nm.

In addition, a 130 nm line and space pattern (a semi dense pattern inwhich the combined total of the resist pattern width and the spacepattern width was 340 nm) was formed with good shape using the sameoperation, and the depth of focus range was 1000 nm.

Furthermore, determination of the 3□ value revealed a result of 5.0 nm.

In addition, in order to evaluate the surface roughness followingetching, the Rms value (root mean square surface roughness) wasdetermined in a similar manner to Example 1, and revealed a result of2.5 nm.

Furthermore, even when the positive type resist composition of thisexample was stored for 60 days at room temperature, the storagestability as a resist solution was good.

Example 6

With the exception of altering the component (C) from Example 5 to amixed solvent of 750 parts by mass of PGMEA and 25 parts by mass of□-butyrolactone, a positive type resist composition was prepared in thesame manner as Example 5.

Furthermore, when pattern formation was conducted under the samelithography conditions as Example 5, the same lithographiccharacteristics as Example 5 were obtained, except for the fact that thesensitivity was 22 mJ/cm².

Furthermore, even when the positive type resist composition of thisexample was stored for 30 days at room temperature, the storagestability as a resist solution was good.

From the results of Examples 5 and 6 it is evident that by using a resinwhich includes a fourth structural unit, in addition to the surfaceroughness effects and the like described above, a positive type resistcomposition can be obtained which also displays excellent resolution forisolated patterns and semi dense patterns.

Example 7

A positive type resist composition was produced by dissolving acomponent (A), a component (B), a component (D) and an additiveuniformly in a component (C), all of which are described below.

-   Component (A): 100 parts by mass of an acrylate ester/methacrylate    ester copolymer (mass average molecular weight: 11,000,    polydispersity: 1.9) formed from the structural units shown below    (x=30 mol %, y=50 mol %, z=20 mol %).-   Component (B): 3.5 parts by mass of    (p-methylphenyl)diphenylsulfonium nonafluorobutanesulfonate-   Component (C): A mixed solvent of 450 parts by mass of propylene    glycol monomethyl ether acetate (PGMEA), 300 parts by mass of    propylene glycol monomethyl ether (PGME), and 25 parts by mass of    □-butyrolactone.-   Component (D): 0.3 parts by mass of triethanolamine.-   Additive: 0.1 parts by mass of a fluorine/silicon based surfactant    R08 (manufactured by Dainippon Ink and Chemicals, Inc.).

An organic anti-reflective film AR-19 (manufactured by Shipley Co.,Ltd.) was provided on top of a silicon wafer at a film thickness of 82nm, and the resist solution described above was then coated onto thisanti-reflective film on the silicon wafer using a spinner, and thendried for 90 seconds at 105□ C on a hotplate (pre bake) to form a resistlayer with a film thickness of 340 nm.

This film was then selectively irradiated with an ArF excimer laser (193nm) through a mask, using an ArF exposure apparatus NSR-S302(manufactured by Nikon Corporation, NA=0.60), subjected to PEB treatmentat 100□ C for 90 seconds, subsequently subjected to puddle developmentfor 30 seconds at 23□ C in a 2.38 mass % aqueous solution oftetramethylammonium hydroxide, and was then washed for 20 seconds withwater, and dried.

As a result, a 130 nm line and space pattern (1:1) was formed with goodshape, and the depth of focus range was 800 nm.

Furthermore, determination of the 3□ value, which is a measure of theLER of the line and space pattern, revealed a result of 6.0 nm.

In addition, in order to evaluate the surface roughness followingetching, the Rms value (root mean square surface roughness) wasdetermined in a similar manner to Example 1, and revealed a result of2.5 nm.

Furthermore, even when the resist solution described above was storedfor 30 days at room temperature, the storage stability as a resistsolution was good.

Example 8

With the exception of replacing 50 parts by mass of the acrylateester/methacrylate ester copolymer used in Example 7 with 50 parts bymass of the quaternary acrylate ester/methacrylate ester copolymer usedin Example 5, and combining the two copolymers to form the component(A), a positive type resist composition was produced in the same manneras Example 7, and pattern formation was also conducted in the samemanner as Example 7.

As a result, the 100 nm isolated line pattern formed by the aboveoperation was formed with good shape, the sensitivity was 23 mJ/cm², andthe depth of focus range was 450 nm. Furthermore, the limitingresolution of the isolated line pattern was 75 nm.

In addition, a 130 nm line and space pattern (a semi dense pattern inwhich the combined total of the resist pattern width and the spacepattern width was 340 nm) produced by the same operation was formed withgood shape using the same operation, and the depth of focus range was1000 nm.

Furthermore, determination of the 3□ value, which is a measure of theLER of the line and space pattern, revealed a result of 5.3 nm.

In addition, in order to evaluate the surface roughness followingetching, the Rms value (root mean square surface roughness) wasdetermined in a similar manner to Example 1, and revealed a result of2.5 nm.

Furthermore, even when the resist solution described above was storedfor 30 days at room temperature, the storage stability as a resistsolution was good.

From the results of Examples 7 and 8 it is evident that in Example 7,which used a resin with 3 structural units, a surface roughnessreduction effect was achieved, and that in Example 8, which used a resinwhich also comprised a fourth structural unit, in addition to the abovesurface roughness reduction effect, a positive type resist compositioncan be obtained which also displays excellent resolution for isolatedpatterns and semi dense patterns. Furthermore, in both Example 7 andExample 8, a mixed solvent of PGMEA and a polar solvent was used, andconsequently the storage stability s was good.

INDUSTRIAL APPLICABILITY

As described above, a positive type resist composition and a resistpattern formation method of the present invention are able to provide achemically amplified positive type resist composition which displayslittle surface roughness and line edge roughness on etching, offersexcellent resolution and a wide depth of focus range, and also enables areduction in the number of defects, as well as a resist patternformation method which uses such a composition.

1. A positive type resist composition comprising (A) a resin componentcomprising within the principal chain a structural unit derived from a(meth)acrylate ester and incorporating an acid dissociable, dissolutioninhibiting group containing a polycyclic group on an ester side chainsection, for which solubility in alkali increases under action of acid,(B) an acid generator component which generates acid on exposure, and(C) an organic solvent, wherein said component (A) comprises astructural unit derived from a (meth)acrylate ester, and comprising anacid dissociable, dissolution inhibiting group containing a polycyclicgroup, a structural unit derived from a (meth)acrylate ester, andcomprising a lactone containing monocyclic group or polycyclic group,and a structural unit derived from a (meth)acrylate ester, andcomprising a hydroxyl group containing polycyclic group; and one of saidstructural units is derived from a methacrylate ester and one of saidstructural unit is derived from an acrylate ester.
 2. A positive typeresist composition according to claim 1, wherein said component (A)comprises a copolymer (A1) with a structural unit derived frommethacrylate ester and a structural unit derived from an acrylic esterand said copolymer (A1) is a copolymer (e) described below: copolymer(e): a copolymer formed from 30 to 60 mol % of a structural unit (a1′)derived from a methacrylate ester, and comprising an acid dissociable,dissolution inhibiting group containing a polycyclic group, 20 to 60 mol% of a structural unit (a2) derived from an acrylate ester, andcomprising a lactone containing monocyclic group or polycyclic group, 1to 30 mol % of a structural unit (a3) derived from an acrylate ester,and comprising a hydroxyl group containing polycyclic group, and 1 to 25mol % of a structural unit (a4) derived from a (meth)acrylate ester, andcomprising a polycyclic group which is different from said aciddissociable, dissolution inhibiting group containing a polycyclic group,said lactone containing monocyclic group or polycyclic group, or saidhydroxyl group containing polycyclic group.
 3. A positive type resistcomposition according to claim 1, wherein said component (B) is an oniumsalt with a fluorinated alkylsulfonate ion as an anion.
 4. A positivetype resist composition according to claim 1, wherein said organicsolvent (C) is a mixed solvent of propylene glycol monomethyl etheracetate and a polar solvent.
 5. A positive type resist compositionaccording to claim 4, wherein said polar solvent is one, or two or moresolvents selected from a group consisting of propylene glycol monomethylether, ethyl lactate and γ-butyrolactone.
 6. A positive type resistcomposition according to claim 1, further comprising (D) a secondary ortertiary lower aliphatic amine in a quantity within a range from 0.01 to0.2 mass % relative to a quantity of said component (A).
 7. A positivetype resist composition according to claim 1, wherein the relativequantities of the structural unit derived from methacrylate ester andthe structural unit derived from acrylate ester within the component (A)are such that relative to the combined number of moles of the structuralunit derived from methacrylate ester and the structural unit derivedfrom acrylate ester, the structural unit derived from methacrylate esteraccounts for 10 to 85 mol %, and the structural unit derived fromacrylate ester accounts for 15 to 90 mol % .
 8. A method of forming aresist pattern comprising the steps of applying a positive type resistcomposition according to claim 1 to a substrate, conducting a prebake,performing selective exposure, conducting post exposure baking, andperforming alkali developing to form a resist pattern.